参数资料
型号: LTC4098EUDC#TRPBF
厂商: Linear Technology
文件页数: 15/32页
文件大小: 0K
描述: IC CHARGER USB COMP 20-UTQFN
标准包装: 2,500
系列: Bat-Track™, PowerPath™
功能: 电源管理
电池化学: 锂离子(Li-Ion)、锂聚合物(Li-Pol)
电源电压: 4.35 V ~ 5.5 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 20-WFQFN 裸露焊盘
供应商设备封装: 20-QFN-EP(3x4)
包装: 带卷 (TR)
LTC4098/LTC4098-1
OPERATION
For very low battery voltages, the battery charger acts like
a load and, due to limited input power, its current will tend
to pull V OUT below the 3.6V instant-on voltage. To prevent
V OUT from falling below this level, an undervoltage circuit
automatically detects that V OUT is falling and reduces the
battery charge current as needed. This reduction ensures
that load current and voltage are always prioritized while
allowing as much battery charge current as possible. Refer
to Overprogramming the Battery Charger in the Applica-
tions Information section.
The voltage regulation loop compensation is controlled by
the capacitance on V OUT . An MLCC capacitor of 10μF is
required for loop stability. Additional capacitance beyond
this value will improve transient response.
An internal undervoltage lockout circuit monitors V BUS and
keeps the switching regulator off until V BUS rises above
the rising UVLO threshold (4.3V). If V BUS falls below the
falling UVLO threshold (4V), system power at V OUT will
be drawn from the battery via the ideal diodes. The volt-
Figures 3 and 4. Bat-Track control circuitry regulates the
external switching regulator’s output voltage to the larger
of BAT + 300mV or 3.6V. This maximizes battery charger
efficiency while still allowing instant-on operation when
the battery is deeply discharged.
When using the LT3480, the feedback network should be set
to generate an output voltage between 4.5V and 5.5V. When
high voltage is applied to the external regulator, WALL will
rise toward this programmed output voltage. When WALL
exceeds approximately 4.3V, ACPR is brought low and the
Bat-Track control of the LTC4098/LTC4098-1 overdrives
the local V C control of the external high voltage step-down
switching regulator. Therefore, once the Bat-Track control
is enabled, the output voltage is set independent of the
switching regulator feedback network.
Bat-Track control provides a significant efficiency advantage
over the simple use of a 5V switching regulator output to
drive the battery charger. With a 5V output driving V OUT ,
battery charger efficiency is approximately:
age at V BUS must also be higher than the voltage at BAT
by approximately 170mV for the switching regulator to
operate.
η TOTAL = η BUCK ?
V BAT
5V
Bat-Track High Voltage External Switching Regulator
Control
The WALL, ACPR and V C pins can be used in conjunction
with an external high voltage step-down switching regulator
such as the LT3653 or LT3480 to minimize heat production
when operating from higher voltage sources, as shown in
SW
LT3653
where η BUCK is the efficiency of the high voltage switching
regulator and 5V is the output voltage of the switching
regulator. With a typical switching regulator efficiency of
87% and a typical battery voltage of 3.8V, the total battery
charger efficiency is approximately 66%. Assuming a 1A
charge current, nearly 2W of power is dissipated just to
charge the battery!
SW
LT3480
I SENSE
V C
FB
V C
HVOK
V OUT
V C
WALL
ACPR
V C
WALL
ACPR
LTC4098/
LTC4098-1
V OUT
SYSTEM
LOAD
LTC4098/
LTC4098-1
V OUT
SYSTEM
LOAD
40981 F03
Figure 3. LT3653 Typical Interface
40981 F04
Figure 4. LT3480 Typical Interface
40981fc
15
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